1. Field of the Invention
The present invention relates to a wireless base station which includes a wired interface and a wireless communication unit which performs wireless communication and controls connection for wireless communication, a wireless network system, a wireless communication method, and a wireless base station control program.
2. Description of the Prior Art
In general, in a wireless network system in which a wireless LAN using wireless transmission as a transmission medium is connected to a wired LAN, when transferring a data frame from the wired LAN to a wireless channel, a wireless base station sends it out as a data frame to which a wireless header storing a basic service set identifier (BSSID) is added.
When a wireless mobile terminal associated with a wireless base station is to transmit a data frame to a wired LAN through the wireless base station, the wireless mobile terminal transmits, to the wireless base station, a data frame to which a wireless header storing the basic service set identifier of the wireless base station with which the wireless mobile terminal is associated is added. With this operation, upon reception of this data frame, the wireless base station transfers the data frame to the wired LAN.
The wireless base station supports switching to another wireless base station and provide mobility by periodically sending out, to the wireless mobile terminal, notification information containing an extended service set identifier (ESSID) or returning an extended service set identifier stored in a management frame corresponding to a request from the wireless mobile terminal and allowing the wireless mobile terminal to identify a distribution system (DS) of its own.
As described above, the wireless mobile terminal participates in a predetermined distribution system by being associated with (association) a wireless base station in which the extended service set identifier registered in a memory of the wireless mobile terminal coincides with the extended service set identifier stored in notification information from the wireless base station or the extended service set identifier stored in a management frame returns in response to a request from the wireless mobile terminal.
When performing so-called wired LAN to wireless LAN bridging, i.e., transferring data frames received from the respective interfaces (a wired LAN and wireless channel) i.e., a wireless communication unit and a wired interface, the wireless base station transmits/receives data frames to which wireless headers storing basic service set identifiers are attached, thereby allowing transfer of the data frames between the wireless base station and the wireless mobile terminal without any connection error in a wireless zone.
In a wireless LAN system using a wireless base station having this wired LAN to wireless LAN bridging function, each wireless mobile terminal makes upper layer settings so as to identify a network, thereby allowing a plurality of wireless mobile terminals to use a single wireless base station as one wireless LAN.
In communication using IP at the upper layer, by assigning 192.168.1.10/24 to the first wireless mobile terminal, 192.168.1.11/24 to the second wireless mobile terminal, and 192.168.1.12/24 to the third wireless mobile terminal, the respective mobile terminals can communicate with terminals and servers connected to the wired LAN through IP in one network through the same wireless base station.
In this wireless LAN system, since a network for each wireless mobile terminal is identified on OSI reference model layer 3 (network layer), when a wireless mobile terminal having a different network address moves to the same wireless base station (roaming), communication cannot be continued.
In addition, when NetBEUI (NetBIOS Extended User Interface) which does not provide a routing function for a network protocol, a broadcast flows between wireless mobile terminals associated with the same wireless base station. This makes it impossible to separate networks, positing a problem in terms of security.
In order to solve such a problem, in a wireless LAN, a layer 2 switch having the VLAN function of separating networks on the data link layer is used to provide a function of logically separating physically identical networks.
A wireless LAN system using wireless transmission as a transmission medium has an acknowledgement function (ACX) or retry function (Retry) to improve the reliability of a transmission path.
Some wireless mobile terminal has a power saving function of suppressing power consumption by intermittently receiving notification information after associated with a wireless base station.
A wireless base station identifies and manages a wireless mobile terminal which performs power saving operation. While the wireless mobile terminal receives no signal, the wireless base station buffers, in its memory, a data frame addressed to the wireless mobile station, and notifies the wireless mobile terminal of information indicating that the data frame is buffered, by using an information element (TIM) of notification information. A broadcast to the wireless mobile terminals associated with the wireless base station is transmitted to each wireless mobile terminal after notification information with a delivery traffic indication message (DTIM) at predetermined intervals.
That is, a wireless mobile terminal designed to perform power saving operation needs to receive notification information with a delivery traffic indication message for the reception of a broadcast.
In order to implement a function of separating networks with which wireless mobile terminals are associated, according to Japanese Unexamined Patent Publication No. 2003-110567 (Reference 1), each of wireless base stations using the same radio frequency includes an embedding unit which requires segment information of a wireless mobile terminal as a transmission target and embeds the information in a frame. According to Japanese Unexamined Patent Publication No. 2003-60656 (Reference 2), networks are separated from each other by associating the MAC addresses of subordinate wireless mobile terminals with VLAN identifiers.
In order to separate wireless networks from each other like wired LANs, a wireless base station must be installed for each network, posing a problem in terms of cost. In addition, since the number of radio frequencies which can be used between a plurality of wireless base stations are limited, it is physically impossible to install such wireless base stations.
In addition, the following problems arise in the network separation scheme according to Reference 1:    (a) Since segment information must be embedded in a frame, a management frame must be modified in accordance with IEEE802.11. That is, this scheme can be applied to only wireless mobile terminals conforming to a special management frame.    (b) Even if networks can be separated from each other between wireless mobile terminals, since the same notification information is used, the terminals operate by using the information element of the notification information. For example, such terminals use common notification information with a delivery traffic identification message which determines the leading edge period of each terminal operating in the power saving mode or a common traffic display message indicating that a data frame is buffered. For example, therefore, even a wireless mobile terminal registered in a network domain with a few broadcasts must be started like a wireless mobile terminal registered in a network domain with many broadcasts, resulting in wasteful power consumption.    (c) When a data network for e-mail, Web browsing, and the like and a network for different characteristics of media such as media for voice communication based on Voice over IP and moving images based on MPEG4 are to be separated and constructed by using this function of separating wireless networks, a predetermined retry count is used as a retry count for data in a conventional wireless base station. If, therefore, the retry count in a data network for which high reliability is required is increased, the increased retry count is applied to a voice data network having priority on real-time performance. As a consequence, a delay due to an error in a wireless zone increases, resulting in a deterioration in real-time performance.    (d) Since wireless mobile terminals are managed by the same wireless base station in different wireless networks, if, for example, the number of wireless mobile terminals associated with each wireless network (Association count) is limited to ensure a wireless zone for voice communication, the number of wireless mobile terminals for a data network is limited in the same manner. This makes it difficult to perform connection management for wireless mobile terminals designed to handle data frames with different characteristics.
In the scheme of separating networks by associating the MAC addresses of wireless mobile terminals with VLAN identifiers in patent reference 2 described above as well, since identical pieces of notification information are used, if, for example, an open authentication algorithm is used for a data network for guests, the open authentication algorithm is applied to another network, posing a problem in terms of security.